docs: def content(self):
          """
          :return: string (unicode) with Dockerfile content
          """
          if self.cache_content and self.cached_content:
              return self.cached_content
  
          try:
              with self._open_dockerfile('rb') as dockerfile:
                  content = b2u(dockerfile.read())
                  if self.cache_content:
                      self.cached_content = content
                  return content
          except (IOError, OSError) as ex:
              logger.error("Couldn't retrieve content of dockerfile: %r", ex)
              raise